1. Technical Field
This application relates to mobile telecommunications systems, for example UMTS (Universal Mobile Telecommunications System), in general and to an apparatus and method for determining whether validity of RAT (Radio Access Technology) handover information in mobile telecommunications system user equipment will remain valid to allow handover from one RAT to another.
2. Description of the Related Art
The approaches described in this section could be pursued, but are not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, the approaches described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.
In a typical cellular radio system, mobile user equipment (UE) communicates via a radio access network (RAN) to one or more core networks. User equipment (UE) comprises various types of equipment such as mobile telephones (also known as cellular or cell phones), lap tops with wireless communication capability, personal digital assistants (PDAs) etc. These may be portable, hand held, pocket sized, installed in a vehicle etc. and communicate voice and/or data signals with the radio access network.
The radio access network covers a geographical area divided into a plurality of cell areas. Each cell area is served by at least one base station, which may be referred to as a Node B. Each cell is identified by a unique identifier which is broadcast in the cell. The base stations communicate at radio frequencies over an air interface with the UEs within range of the base station. Several base stations may be connected to a radio network controller (RNC) which controls various activities of the base stations. The radio network controllers are typically connected to a core network.
UMTS is a third generation public land mobile telecommunication system. Various standardization bodies are known to publish and set standards for UMTS, each in their respective areas of competence. For instance, the 3GPP (Third Generation Partnership Project) has been known to publish and set standards for GSM (Global System for Mobile Communications) based UMTS, and the 3GPP2 (Third Generation Partnership Project 2) has been known to publish and set standards for CDMA (Code Division Multiple Access) based UMTS. Within the scope of a particular standardization body, specific partners publish and set standards in their respective areas.
Consider a wireless mobile device, generally referred to as user equipment (UE), that complies with the 3GPP specifications for the UMTS protocol. The 3GPP 25.331 specification, referred to herein as the 25.331 specification, addresses the subject of UMTS RRC (Radio Resource Control) protocol requirements between the UMTS Terrestrial Radio Access Network (UTRAN) and the UE.
Clause 8.1.1 of the 25.331 specification, relates to the broadcast of system information. The UTRAN—that part of a UMTS network which consists of one or more RNC and one or more Node B between Iu and Uu interfaces—sends system information to a UE by means of a message that comprises a Master Information Block (MIB) and a plurality of System Information Blocks (SIBs). The MIB provides references and scheduling information for a number of system information blocks. A system information block groups together system information elements (IEs) of the same nature. Different system information blocks may have different characteristics, e.g. regarding their repetition rate and the requirements on UEs to re-read the system information blocks. The system information blocks contain the actual system information. The master information block may optionally also contain reference and scheduling information to one or two scheduling blocks, which give references and scheduling information for additional system information blocks. Scheduling information for a system information block is included in either the master information block or one of the scheduling blocks.
When a UMTS cell is selected by a mobile device, the master information block (MIB) is read on the broadcast control channel (BCCH) followed by the appropriate system information blocks (SIBs).
If the Universal Terrestrial Radio Access Network (UTRAN) needs to change any of the system information blocks, it informs the mobile devices (UEs) in the cell. This is achieved by the UTRAN sending SYSTEM INFORMATION as illustrated generally in FIG. 1. Upon modification of system information blocks using value tags, UTRAN notifies the new value tag for the master information block in the IE “BCCH modification info”. As illustrated in FIG. 2, a message advising this is transmitted to the UE. When the UE is in idle mode, CELL_PCH state and URA_PCH state, the IE “BCCH modification info” is contained in a PAGING TYPE 1 message transmitted on the PCCH in all paging occasions in the cell. When the UE is in CELL_FACH state or TDD UEs in CELL_DCH with S-CCPCH assigned, the IE “BCCH modification info” is contained in a SYSTEM INFORMATION CHANGE INDICATION message transmitted on the BCCH mapped on at least one FACH on every Secondary CCPCH in the cell. Upon reception of a PAGING TYPE 1 message or a SYSTEM INFORMATION CHANGE INDICATION message containing the IE “BCCH modification info” containing the IE “MIB value tag” but not containing the IE “BCCH modification time”, the UE performs the actions as specified in subclause 8.1.1.7.3 of the 25.331 specification. If the IE “BCCH modification time” is included the UE shall perform actions as specified in subclause 8.1.1.7.2 of the 25.331 specification.
In part 8.1.1 of the 25.331 standard (for instance, Clauses 8.1.1.1.4, 8.1.1.5 and 8.1.1.6) it is stated that a UE may consider the content of the scheduling block or system information block as valid until it receives the same type of block or at most six hours after reception.
Many user equipment devices in the UTRAN may be configured to operate in more than one radio access technology (RAT), for example the user equipment devices may be configured to operate in GSM as well as UMTS. System Information Block 16 (SIB16) contains radio bearer, transport channel and physical channel parameters to be stored by the user equipment device in idle and connected modes for use during handover to UTRAN. For all SIBs except SIB types 15.2, 15.3 and 16 the content is the same in each occurrence for SIBs using a value tag. SIB types 15.2, 15.3 and 16 may occur more than once (that is, more than one version of these SIBs may be stored on a UE) with different contents. In this case, scheduling information is provided for each such occurrence of these SIBs. SIBs that do not use a value tag may have a different content for each occurrence.
Clause 8.1.1.6.16 of the 25.331 standard defines the requirements for multiple occurrences of SIB16 stored in the UE, one for each predefined configuration for the UE: that is, for each predefined communication mode (voice, data), various data transfer rates, etc. These configurations are defined in clause 10.3.4.5 of the 25.331 specification and numbered 0 . . . 15 (zero to fifteen). A UE configured to operate in more that one RAT may be required to handover its mode of operation from a first RAT (for example, GSM) to a second RAT (for example, UMTS). Such a requirement to hand over may happen in either idle or connected mode. In these circumstances, UTRAN requests of the UE details of which occurrences of SIB16 are stored in the UE, so UTRAN can select one of these for use in the handover. The SIB16s are stored in the UE in the form of an identifier (ID) for each occurrence of the SIB16 (a four-bit number) along with the SIB16 configuration data itself (comprising of the order of 100 bytes of data). The request by UTRAN is sent in the form of a Inter RAT Handover Info (IRHI) request message, the response to which is generally illustrated in FIG. 3. This response is implemented by the UE transmitting to UTRAN details of the SIB16s stored on the UE (which may include an ID for the SIB16s). As the UE is operating in a RAT other than UMTS, the IRHI request and response thereto must be transmitted via the other RAT, in this example, GSM.
Upon receipt of a IRHI message from the UE, UTRAN then selects which of the SIB16s is to be used in the handover. UTRAN chooses an appropriate configuration for an inter-RAT handover depending on any or all of a number of factors, including the capabilities of the UE, the purpose of the connection and the loading on UTRAN. Following this, UTRAN instructs the UE to use the selected occurrence of SIB16, communicating the reference number/identifier 0 . . . 15 of the selected SIB16 to the UE to use that SIB16 when executing the handover.
During execution of a RAT handover, problems may occur when, for example, the UE informs UTRAN that SIB16_7 (that is, an occurrence of the eighth type of SIB16 for an eighth predefined configuration of operation of the UE) is stored on the UE. However, situations may arise when the validity of that occurrence of SIB16 is about to expire, but UTRAN is unaware of this and proceeds to instruct the UE to execute a RAT handover using that particular SIB16 at a time after which the validity of SIB16_7 has expired. In such a circumstance, the UE is required to reject the handover attempt and send a handover failure message to the GSM Edge Radio Access Network (GERAN) on the GSM interface. UTRAN may then proceed in any of a number of different ways. For instance, UTRAN may instruct the UE to execute an RAT handover using a default configuration which does not expire, or it may send a further request for IRHI, in which case the UE will respond by re-transmitting further information relating to valid SIB16s stored on the UE for UTRAN to choose. However, there is again the risk that UTRAN will select an SIB16 which is about to expire and, if the UE is instructed to handover using an SIB16 which has then expired, the UE is required to reject the handover attempt and send a handover failure message to GERAN.
A possible partial solution to this problem arising in such situations is to avoid allowing the SIBs to expire by utilising the methods and apparatus of commonly-assigned U.S. patent application Ser. No. 10/775,030 and European Patent Publication No. 1562387. If an SIB is set to expire six hours after it is read, then re-reading it, say, five hours after being previously read means that it will then be valid for another six hours. Thus, the SIB will never expire if the process is repeated in this manner. However, if the SIB is unable to be re-read, then problems might arise. For instance, if no UMTS coverage is available until after a communication on the UE has commenced, trying to prevent SIB16s expiring will be unsuccessful as it is may not be possible for some UE devices to read SIBs during a call.
There are therefore proposed strategies for determining whether RAT handover information will remain valid within an expiry period. A number of such strategies are detailed below.
Other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of an apparatus and method for querying for RAT handover information in mobile telecommunications systems such as UMTS.
The same reference numerals are used in different figures where appropriate to denote similar elements.